The present invention relates to a control device and method for an internal combustion engine equipped with a fuel injection system; and more particularly relates to a control device, incorporating a plurality of sensors and an electronic control computer which receives signals from said sensors and which controls said fuel injection system of said internal combustion engine, said control device accurately and appropriately controlling the amount of fuel supplied by said fuel injection system during acceleration of the internal combustion engine when the engine is not yet fully warmed up so as to provide good engine accelerating characteristics, and to a control method for said internal combustion engine equipped with a fuel injection system, said control method being practiced by said device.
Fuel injection is becoming a more and more popular method of fuel supply to gasoline internal combustion engines of automotive vehicles nowadays. This is because of the inherently greater accuracy of metering of liquid fuel by fuel injection techniques as opposed to the metering of liquid fuel available in a carburetor type fuel supply system. In many cases the advantages obtained by this greater accuracy of fuel metering provided by a fuel injection system outweigh the disadvantage of the increased cost thereof. For example, this better fuel metering enables engine designers to produce engines with higher compression ratio and more spark advance, which can lead to increased performance characteristics, such as increased power, increased torque, and better engine elasticity.
Because a fuel injection system can accurately determine the amount of fuel to be supplied to the intake system of the vehicle in a wide variety of engine operational conditions, it is possible to operate the engine in a way which generates substantially lower levels of harmful exhaust emissions such as NOx, HC, and CO; and in fact it is possible to satisfy the legal requirements for cleanliness of vehicle exhaust gases, which are becoming more and more severe nowadays, without providing any exhaust gas recirculation for the engine. This is very beneficial with regard to drivability of the engine, especially in idling operational condition. Further, because of the higher efficiency of fuel metering available, this allows a leaner adjustment of the engine with still acceptable drivability. With fuel injection provided to a vehicle type, more consistent exhaust emission results are available from vehicles coming off the assembly line at the factory, without complicated, troublesome, and expensive individual adjustments. Further, the warmup control of the vehicle is highly flexible, i.e. can be flexibly adjusted to a wide variety of warming up conditions, which contributes considerably to the achieved exhaust emission results.
Further, an internal combustion engine equipped with a fuel injection system can be operated in such a way as to be substantially more economical of gasoline than a carburetor type internal combustion engine. This is again because of the greater accuracy available for determination of the amount of fuel to be supplied to the intake system of the vehicle over a wide variety of engine operational conditions. Since it is possible to operate the engine at the stoichiometric air/fuel ratio, and to apply closed loop control to the fuel injection control system, it is possible to reduce the spark retardation, and the above mentioned dispensing with exhaust gas recirculation is possible, which has a significant beneficial effect with regard to fuel consumption. Further, with fuel injection, it is possible to cut off fuel supply entirely when the engine is operating in an overrun mode, which again results in a significantly reduced consumption of fuel. Nowadays, with the increased costs of fuel and the wider demand for fuel economical vehicles, and with legal requirements which are being introduced in some countries relating to fuel economy of automotive vehicles, these considerations are more and more becoming very important. In addition, by the introduction of fuel injection, a engine of smaller piston displacement can replace an engine with larger piston displacement which is provided with a carburetor type fuel supply system, while providing the same output power, and again this reduces fuel consumption. By the introduction of fuel injection, also, in many cases it is possible to switch an engine from premium grade type fuel operation to operation on lower grade or regular type fuel, while providing the same output power, which is economical of the more expensive premium grade type fuels.
Some types of fuel injection system for internal combustion engines utilize mechanical control of the amount of injected fuel. An example of this mechanical fuel amount control type of fuel injection system is the so called K-jetronic type of fuel injection system. However, nowadays, with the rapid progress which is being attained in the field of electronic control systems, various arrangements have been proposed in which electronic control circuits make control decisions as to the amount of fuel that should be supplied to the internal combustion engine, in various engine operational conditions. Such electronic fuel injection systems are becoming much more popular, because of the more flexible way in which the fuel metering can be tailored to various different combinations of engine operational conditions. The most modern of these electronic fuel injection systems use a microcomputer such as an electronic digital computer to regulate the amount of fuel injected per one engine cycle, and it is already conventionally known to use the microcomputer also to regulate various other engine functions such as the provision of ignition sparks for the spark plugs.
In an electronic fuel injection system, the control system requires of course to know the moment by moment current values of certain operational parameters of the internal combustion engine, the amount of injected fuel being determined according to these values. The current values of these operational parameters are sensed by sensors which dispatch signals to the electronic control system via A/D converters and the like. In such an arrangement, electric signals are outputted by such an electronic control system to an electrically controlled fuel injection valve, so as to open it and close it at properly determined instants separated by a proper time interval; and this fuel injection valve is provided with a substantially constant supply of pressurized gasoline from a pressure pump. This pressurized gasoline, when the fuel injection valve is opened, and during the time of such opening, is squirted through said fuel injection valve into the intake manifold of the internal combustion engine upstream of the intake valves thereof. Thus, the amount of injected gasoline is substantially proportional to the time of opening of the fuel injection valve, less, in fact, an inoperative time required for the valve to open. Sometimes only one fuel injection valve is provided for all the cylinders of the internal combustion engine, or alternatively several fuel injection valves may be provided, up to one for each cylinder of the engine, according to design requirements.
The first generation fuel injection systems were of the so called D-jetronic type, in which the main variables monitored by the electronic fuel injection control system were the revolution speed of the internal combustion engine and the vacuum, or depression, present in the intake manifold of the internal combustion engine due to the suction in said intake manifold produced by the air flow passing through the intake manifold of the internal combustion engine to enter the combustion chambers thereof after being mixed with liquid fuel squirted in through the fuel injection valve or valves. From these two basic measured internal combustion engine operational parameters, a basic amount of gasoline to be injected into the intake system of the internal combustion engine is determined by the control system, and then the control system controls the fuel injection valve so as to inject this amount of gasoline into the engine intake system. Other variables, such as intake air temperature, engine temperature, and others, are further measured in various implementations of the D-jetronic system and are used for performing corrections to the basic fuel injection amount.
Following this, a second generation of fuel injection systems has been developed, which is of the so called L-jetronic type, in which the main variables monitored by the electronic fuel injection control system are the revolution speed of the internal combustion engine and the amount of air flow passing through the intake manifold of the internal combustion engine to enter the combustion chambers thereof after being mixed with liquid fuel squirted in through the fuel injection valve or valves. This air flow amount is measured by an air flow meter of a design which has become developed. From these two basic measured internal combustion engine operational parameters, again a basic amount of gasoline to be injected into the intake system of the internal combustion engine is determined by the control system, and then the control system controls the fuel injection valve so as to inject this amount of gasoline into the engine intake system. Other variables, such as intake air temperature, engine temperature, and others, are again further measured in various implementations of the L-jetronic system, and are used for performing corrections to the basic fuel injection amount. This L-jetronic fuel injection control system is currently well known and is nowadays fitted to a large number and variety of vehicles.
One refinement that has been made to the L-jetronic fuel injection system has been to perform a control of the fuel injection amount based upon feedback from an air/fuel ratio sensor which is fitted to the exhaust manifold of the internal combustion engine and which detects the concentration of oxygen in these exhaust gases, again in a per se well known way. This feedback control homes in on a proper amount of fuel injection to provide a stoichiometric air/fuel ratio for the intake gases sucked into the cylinders of the engine, and for the exhaust gases of the engine, but the starting point region over which the homing in action of the feedback control system is effective is limited, and therefore the determination of the approximately correct amount of fuel to be injected by the fuel injection valve is still very important, especially in the case of transient operational conditions of the engine.
One difficulty that has occurred with such normal spark ignition engines which are equipped with the L-jetronic form of electronic fuel injection system is that, when the engine is not yet fully warmed up to operational temperature and then is accelerated, proper engine acceleration is not fully obtained. It has been determined experimentally that this problem of improper engine acceleration can be at least partially cured by increasing the amount of fuel injected into the internal combustion engine at this time. Accordingly, a requirement has arisen for a fuel injection system which can provide this extra fuel injection supply at times of acceleration when the internal combustion engine is not yet fully warmed up.
Further, it has been also experimentally determined that it is desirable for the amount of this cold acceleration extra injected fuel to be gradually and progressively decreased as the acceleration of the internal combustion engine progresses. This is particularly helpful with regard to diminishing of the amount of harmful pollutants emitted in the exhaust of the internal combustion engine, in particular HC and CO. Thus, further a requirement has arisen for a fuel injection system which can provide this diminishing of the extra fuel injection supply at times of acceleration when the internal combustion engine is not yet fully warmed up.
With regard to such requirements, the question arises as to how the fuel injection system control system can acquire information as to whether or not, and when, the internal combustion engine is being operated in a acceleration operational condition. This information could be provided to the fuel injection system by providing a throttle position sensor for detecting the amount of throttle opening of the vehicle; but such a throttle position sensor is costly, involves additional problems during assembly and maintenance of the fuel injection system, and further is liable to breakdown. Further, since for the best possible acceleration detection such a throttle position sensor needs to be one from whose output signal even partial acceleration of the vehicle can be detected, in other words needs to be one whose signal is indicative not only of acceleration which is produced by opening of the vehicle throttle from the fully closed position but also of acceleration which is produced by opening of said vehicle throttle from a partially open position, a siimple throttle limit switch which only detects full closing of the vehicle throttle is not really adequate for this purpose.